The eight U.S. troops were killed in separate bomb attacks in southern Afghanistan against Stryker Armored Vehicles that also killed one Afghan civilian. There were at least three Americans injured as a result of today's attacks.

Combined with the deaths Monday of 11 U.S. servicemen and three agents from the Drug Enforcement Administration in separate helicopter crashes, 22 Americans have been killed in Afghanistan in the past two days.

The Taliban had claimed responsibility for downing a Chinook MH-47 helicopter in western Afghanistan Monday, but Defense Department officials said today that there are no indications that any of the helicopter crashes yesterday were caused by hostile fire.

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Violence levels against American and NATO troops spiked this summer following the arrival of 21,000 U.S. troops ordered as reinforcements by the Obama administration. There are now 68,000 U.S. troops in Afghanistan and 32,000 NATO troops.

The year's previous monthly high was in August around the time of Afghanistan's presidential vote in August, when 51 U.S. soldiers died. October's death toll is already higher than the number of U.S. fatalities in each of the years from 2001 to 2004.

Defense officials tell ABC News that today's fatalities occurred in two separate, but similar attacks on the Army's armored vehicles known as Strykers.

The most devastating attack occurred in northwest Kandahar province where seven troops died when a Stryker vehicle was blasted by a roadside bomb explosion that was followed by small arms fire. The military labels these types of attacks as complex because they involve more than one form of attack.

Today's other U.S. fatality occurred when another Stryker vehicle operating in Zabul province which is next to Kandahar province was struck by a roadside bomb.

Casualty Levels Rise in Afghanistan War

There is only one Army Stryker unit operating in Afghanistan, the 5th Stryker Brigade, 2nd Infantry Division which is based at Fort Lewis, Wash.

The Stryker brigade was scheduled to deploy to Iraq this summer, but was diverted to Afghanistan because their speed and maneuverability would allow greater coverage area along with armored protection.

White House Press Secretary Robert Gibbs offered a statement to today's loss of life in Afghanistan.

"As always our prayers go out to those who have lost a loved one and for those who sacrificed so much to serve our country"said Gibbs.

The DEA released the names of the three agents who died in Monday's helicopter crash. They Special Agent Forrest N. Leamon, 37, of Woodbridge, Va., and Special Agent Chad L. Michael, 30, of Quantico, Va. Both are members of the DEA's FAST, or Foreign-deployed Advisory and Support Teams.

The third agents was identified as Special Agent Michael E. Weston, 37, of Washington, D.C., who had been assigned to the DEA's Kabul office.

Separately, the U.S. military said it had also recovered the bodies of three civilians who had been missing in the mountains of northeast Afghanistan since Oct. 13, when the Army C-12 Huron plane they were piloting had crashed.